I don't think anyone has an offline transaction service yet.
so far we can only transact if we are connected to the internet, but if the internet is off we can't
do anything.
This project is very useful if the internet is off, we can still make transactions. I think someone must have thought about it
it may still be under development. At the moment I know of only crypto wallets that can store coins offline in a dedicated hardware wallet.
Hopefully in the future it can be realized transacting offline.